The objective of this proposal is to elucidate the metabolic and immunological consequences of adenosine deaminase deficiency in lymphocytes. Lack of a functional form of this enzyme has recently been associated with a distinctive type of combined immunodeficiency. Delineation of the role of this enzyme in formal lymphocytes will provide additional information relevant to basic lymphocyte metabolism and may lead to new approaches for the treatment of lymphoid malignancies. Potent adenosine deaminase inhibitors will be employed to mimic the enzymic defect in normal lymphocytes. The block in adenosine catabolism is expected to result in increased levels of the nucleoside. Exogenous adenosine has previously been shown to be toxic to normal cells, toxicity being attribued to pyrimidine starvation. In addition, the nucleoside has a modulating influence on the cAMP levels in other cell systems. In order to achieve our objectives we will: (1) quantitate endogenous production of adenosine in lymphocytes in the presence and absence of inhibitors of adenosine deaminase; (2) determine the effects of adenosine on intracellular levels of phosphoribosyl pyrophosphate and clyclic nucleotides; (3) assay enzymes related to adenosine metabolism; (4) quantitate nucleotide and nucleoside pools in lymphocytes using high pressure liquid chromatography to evaluate the effects of adenosine deaminase inhibition, and (5) relate the metabolic effects of ADA inhibition to the ability of the lymphocyte to express various immunological functions including a) in vitro immune responses, b) response to various mitogens, and c) response in mixed lymphocyte cultures.